The invention relates generally to wireless communications and, more particularly, to the use of Medium Access Control (MAC) states during CDMA wireless communications.
Code Division Multiple Access (CDMA), also referred to as xe2x80x9cspread spectrumxe2x80x9d, has become a well-known method by which wireless communications are implemented. In a CDMA wireless communications network, a form of multiplexing is used whereby a transmitter at a base station encodes a signal using a pseudo-random sequence which a mobile station of a user also knows and can use to decode the signal when the signal is received. In some CDMA implementations, each pseudo-random sequence used by the base station contains a finite length sequence, known as a Walsh code. The Walsh codes used by a particular base station are mutually orthogonal, which allows a user of a particular code to receive his or her desired signal from the base station without interference from other users served by the same base station. Interference between users served by the same base station is known as intra-cell interference.
Each Walsh code corresponds to a different communication channel. As a consequence, the number of channels which may be used in CDMA without intra-cell interference is limited to the number of Walsh codes which are available. The number of available Walsh codes is limited by available bandwidth and interference considerations. Given conventional bandwidth limitations, there are 128 orthogonal Walsh codes and, thus, 128 channels of communication, available for use in CDMA.
Because there are often more mobile stations that desire a channel and, hence, a Walsh code, than there are Walsh codes available, users of mobile stations must often wait until a Walsh code becomes available to make or receive a call on a mobile station. In an attempt to resolve this problem, quasi-orthogonal functions have been developed to generate more than 128 Walsh codes. Because conventional quasi-orthogonal functions are not truly orthogonal, the channels using such Walsh codes significantly increase interference for every mobile station being served by a particular base station in a CDMA network. When interference increases, transmission power must be increased. As transmission power is increased, the number of mobile stations which may be served by a base station in a CDMA network without waiting for a Walsh code to become available decreases.
Therefore, what is needed is a method by which an increased number of mobile stations may be served in a CDMA network without generating additional interference.
The present invention, accordingly, provides a method for sharing Walsh codes between at least two mobile stations operating simultaneously in a Control Hold Medium Access Control (MAC) state in Code Division Multiple Access (CDMA), whereby, upon entry of a respective mobile station into the Control Hold MAC state, a gating rate of 1/xc3x97 to be used by the respective mobile station is determined, wherein xc3x97 is greater than one. A Walsh code being used by less than xc3x97 mobile stations in the control hold MAC state is identified and allocated to the respective mobile station to thereby define a channel of communication for the respective mobile station. A time slot which is not being used by any mobile stations using the identified Walsh code in the control hold MAC state, is identified and allocated to the respective mobile station, thereby permitting at least one signal to be transmitted between a base station and the respective mobile station using the identified Walsh code during the time slot allocated to the respective mobile station.
By the use of the present invention, transmitted power on the forward link and reverse link is reduced over the prior art, thereby resulting in less interference and more network capacity. Furthermore, the limited number of Walsh codes is more efficiently used, thereby further increasing capacity.